The present invention relates to radio communication networks and in particular to a method for synchronizing terrestrial nodes equipped with GNSS (Global Navigation Satellite System) receivers and belonging to a terrestrial network.
In terrestrial networks, especially radio communication networks, the synchronization of the different elements belonging to the network (i.e. base stations, mobile stations) is of crucial importance for a proper working of the network. Known methods for synchronization in a radio communication network consist in that the terrestrial nodes of the network communicate to synchronize. This kind of auto-synchronization of a network is subject to the variations of the radio link quality. Moreover, the distance between the network nodes should be known with a high accuracy in order to deduce the transmission delay between the network nodes and obtain a good synchronization precision.
More precise synchronization may be obtained if the network nodes are additionally equipped with GNSS receivers. A GNSS system enables the synchronization of a terrestrial terminal with a common time reference shared by the satellites of the GNSS constellation. For a proper synchronization, GNSS signals emitted by three different satellites of the GNSS constellation have to be received simultaneously at the terrestrial terminal equipped with GNSS receiver. Then, it is a usual functionality of a GNSS receiver to correlate these 3 GNSS signals to estimate the local time.
However, this time reference acquisition procedure is long (about 1 minute) especially in urban area where the clear sky angle seen by the terrestrial station is reduced. Then, a configuration where 3 satellites can be viewed in this narrow clear sky angle is often long to be obtained.
Moreover, the accuracy of the estimated local time is limited by the accuracy of the time reference emitted by the satellite (e.g. 10-4 s).
A particular object of the present invention is to provide a method for synchronizing terrestrial terminals equipped with a GNSS receiver and belonging to a terrestrial network faster and with a higher accuracy than with the known prior art methods
Another object of the invention is to provide a terrestrial node and adapted to perform such a synchronization method.